I tried smiling at everyone all day — here's how it affected my outlook on life

It might not even have to be genuine to have an impact on how you feel.

I tried smiling all day to see if I felt any more optimistic.

Fake smiles might help with a stressful situation, but otherwise, I wasn't convinced.

To get the most benefits from a smile, it probably has to be genuine.

Someone's smile can reveal a lot. Sometimes they are sincere, while other times they may be covering up pain, embarrassment, or rage.

As a species, humans are generally pretty good at picking up on whether someone's smile is real or not. I don't tend to believe flight attendants really are that pleased to see me. Whereas with my friends, I'd be pretty surprised to find out they've been lying to me this whole time about how much they enjoy my company.

Regardless of the feelings underneath our expression, a smile may be able to make us feel better. Various studies have found that smiles can boost our mood, send pleasure signals to our brains, and even improve our relationship longevity. So to (very unscientifically) test the theory, I put smiling on trial.

My smiles often come easily when I'm with friends or thanking someone for serving me coffee, but it's harder the rest of the time. While in transit, for instance, I rarely see a smile exchanged between people. On the tube in London, it's almost frowned upon to even look someone in the eye — let alone grin at them.

As a result, I stay stony-faced when walking around the city or getting on a train, simply because it's the status quo, and it would feel weird to do anything else. It's quite possible that my sour face might be having an impact on my mood, so I tried smiling at everyone I saw all day to see if it had any impact on my outlook on life.

My immediate reaction was that it was uncomfortable. Making a concerted effort to smile suddenly made it feel awkward and superficial — which I guess is exactly what it was.

The day started fairly regularly. I got up, made breakfast, and headed out for a run. I didn't feel like smiling while panting around the park, but I tried my best. I don't think people were expecting me to lock eyes with them and smile while they were also exercising, but I didn't get any reactions that suggested they were too alarmed by it.

Afterwards, I showered and headed out for the day, catching a few smiles from others on the way to the tube station. I wondered if they were reflecting my positive spirit, but then again, they might have been a bit more forthcoming considering it was a Saturday.

Smiling at people on the tube was more difficult, and I didn't have much luck with sending my positivity out into the world. I had a short journey into town, but everyone around was either reading or on their phone. Even if I did meet someone eye to eye, they immediately looked away. Not exactly an ego boost.

After a fairly disappointing journey, I saw some friends, and forgot about my experiment, but I'm pretty sure I smiled most of the time. The only other strangers I saw in close enough proximity to smile at were some bartenders and an Uber driver. The former was met with little more than a lip curl, and in the Toyota Prius at 1 a.m., it was too dark to see if the driver smiled back.

Ultimately, I went to bed in a fairly good mood. But as previously mentioned, it was a Saturday, which could mean I was simply in better spirits anyway. How could I tell if my extra smiling had any impact? Science might be able to help work it out.

Our exterior can influence how we feel inside

Charles Darwin was one of the first people to note how our outside appearance can influence how we feel inside.

"The free expression by outward signs of an emotion intensifies it," he wrote in 1872. "On the other hand, the repression, as far as this is possible, of all outward signs softens our emotions."

In other words, smile, it might never happen.

Other research has shown how our exterior impacts how we feel, such as how certain colours can make people feel more confident, or even run faster.

So even if I couldn't feel it, smiling may have been having a slight psychological impact on how I dealt with stress throughout the day. That might be more obvious if I was more jovial in the long term, rather than just smiling more for a single day.

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You can't beat the real thing

You may notice that it's hard not to smile when other people do. Research has shown that smiling can actually be contagious, and one study, published in Trends in Cognitive Sciences, explained a theory for why this is: mimicking other people's facial expressions helps us empathise with their feelings.

But what does that say about a forced smile? Do people mimic those too? Or did fewer people catch my smiles throughout the day because it was clearly insincere?

There are multiple types of smiles, according to psychologists — each conveying something a little bit different.

In the 19th century, a French neurologist called Guillaume Duchenne divided smiles into two categories: real smiles that crinkle the eyes, called "Duchenne smiles," and fake ones that only move the mouth muscles, called "Pan Am smiles."

A BBC article from 2017 suggests there could be as many as 19 smile sub-types, but only six of them are used when we're genuinely happy. Others, like the embarrassed smile, the contempt smile, and the fake smile are all used with something else under the surface.

I don't know where my "smiling for the sake of an experiment" smile fits on that scale. But if I had to guess, it would be that the emotion I was trying to get across wasn't totally genuine. It's quite possible that passersby picked up on this — the ones who looked at me anyway — and if I wanted to really spread the joy, my smile had to come from somewhere real.

It's also possible that the stress of engaging with other Londoners probably outdid any psychological benefit I may have felt anyway.

Either way, I'm happy to try out smiling the next time something is stressing me out, or I need to give myself a mood boost, just in case it works. But when it comes to other people, and how you interact with them, perhaps a plastic smile doesn't really do that much good. Perhaps they actually need to be real.